In future, in addition to renewable energy (solar power generation, wind power generation, or the like), lots of power supplies (output variation type power supplies) whose outputs fluctuate depending upon weather are expected to be employed in large quantity in a power system. In addition, recently, power liberalization has been proceeded in the world, and as a result, facility investment of the power system is suppressed, and a power flow flowing through an existing transmission line increases (becomes a heavy tide). If tide variation (tide change) increases in a heavy tide state, voltage stability of a power system can deteriorate. Furthermore, if the system fails due to lightning strike or the like, voltage stability of the power system can further deteriorate. It is necessary to provide a voltage stability monitoring device which can accurately monitor a deterioration phenomenon of the voltage stability.
A background technique of the present technical field is descried in, for example, Mamoru Suzuki, Yukio Kishida: “Voltage Stability Online Monitoring System”, Institute of Electrical Engineers of Theory B, Vol. 111, No. 3, 1991 (NPL 1). The review paper describes “Online Periodic Monitoring Function” and “Stability Determining Function at the Time of Peak Load” (refer to pp. 248-251 of text).
In addition, there is JP-A-2011-115024 (PTL 1). In PTL 1, a voltage reactive power monitoring system is described which coincides with motion of entirety of an actual power system in a case of being viewed from the entire power system, by determining a P-V curve after optimal tide calculation is performed to minimize a predetermined object function, or setting state variables of the entire load buses which are involved in a power system within a predetermined specified value.
In addition, there is JP-A-2005-287128 (PTL 2). In PTL 2, a power system stability monitoring system is described which can monitor stability of a system voltage while also accurately following control of a transformer tab or the like, since a P-V curve is drawn with high accuracy and at a high speed and the P-V curve traces a continuous load.